Document WebMvcProperties.MatchingStrategt as being since 2.4.0

Closes gh-24875

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/servlet/WebMvcProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -533,6 +533,10 @@ public class WebMvcProperties {
 
 	}
 
+	/**
+	 * Matching strategy options.
+	 * @since 2.4.0
+	 */
 	public enum MatchingStrategy {
 
 		/**